U.S. Pat. No. 4,687,017, for example, discloses a fluid control device in the form of a control valve in which a sealing assembly of the general type described above is used. The device described therein comprises a valve body with a valve chamber that is open at one end. A closing piece with a flange of enlarged diameter is placed over the open end. To achieve the seal between the flange and the valve body, the flange is provided with a rounded annular bead seal along its circumference at the lower side. The (rounded) bead seal is in contact with a planar shoulder formed at the valve body. An internally threaded gland nut cooperates with a screw thread externally provided on the valve body so as to exert an axial compression force on the bead seal. Although a reasonable degree of sealing can indeed be achieved with the above construction without the use of an 0-ring, it was found in practice that that the construction is not satisfactory if the components are to be detached from one another and fastened again a number of times (so-termed re-assembly). This, however, may be useful both during production and during maintenance.